MEASUREMENT AND MODELING OF THE MILLIMETER-WAVE BACKSCATTER RESPONSE OF SOIL SURFACES

The millimeter-wave (MMW) backscatter response of bare-soil was examin ed by conducting experimental measurements at 35 and 94 GHz using a tr uck-mounted polarimetric scatterometer and by developing appropriate m odels to relate the backscattering coefficient to the soil's surface a nd volume properties, The experimental measurements were conducted for three soil surfaces with different roughnesses under both dry and wet conditions, The experimental measurements indicate that in general th e backscattering coefficient is comprised of a surface scattering comp onent sigma(s) and a volume scattering component sigma(v). For wet soi l conditions, the backscatter is dominated by surface scattering, whil e for dry conditions both surface and volume scattering are significan t, particularly at 94 GHz, Because theoretical surface scattering mode ls were found incapable of predicting the measured backscatter, a semi empirical surface scattering model was developed that relates the surf ace scattering component of the total backscatter to the roughness par ameter ks, where k = 2 pi/lambda and s is the rms height, and the diel ectric constant of the soil surface, Volume scattering was modeled usi ng radiative transfer theory with the packed soil particles acting as the host material and the air voids as the scattering particles, The c ombined contribution of surface and volume scattering was found to pro vide good agreement between the model calculations and the experimenta l observations.